Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.66   9.175%   $35.6566   $35.66   $35.65   $35.70  
  Purchase #2 $19.67   13.671%   $22.3591   $22.36   $22.35   $22.40  
  Purchase #3 $163.95   11.354%   $182.5649   $182.56   $182.55   $182.60  
  Purchase #4 $15.84   8.782%   $17.2311   $17.23   $17.25   $17.20  
  Purchase #5 $227.36   10.192%   $250.5325   $250.53   $250.55   $250.50  
  Purchase #6 $243.74   8.807%   $265.2062   $265.21   $265.20   $265.20  
  Purchase #7 $73.80   3.338%   $76.2634   $76.26   $76.25   $76.30  
  7 purchase totals = $777.02       $849.8138   $849.81   $849.80   $849.90